FUNCTION: Perm2Code - calculate the code of a permutation

CALLING SEQUENCE:

Perm2Code(perm)

SG[Perm2Code](perm)

PARAMETERS:

perm = any list denoting a permutation

SYNOPSIS:

• The Perm2Code function calculates the Lehmer code of a permutation.

• Let [c1, c2, ...] be the code of perm, then ci is equal to the number of indices j>i such that perm[j]<perm[i].

• Whenever there is a conflict between the function name Perm2Code and another name used in the same session, use the long form SG['Perm2Code'].

EXAMPLES:

> with(SG):
> Perm2Code([4,1,5,2,3]);
 
                                 [3, 0, 2, 0, 0]
 
> Code2Perm([3, 0, 2, 0, 0]);
 
                                 [4, 1, 5, 2, 3]